This invention relates to a safety syringe with retractable needle, and a method for delivering fluids to a patient and retracting the needle within the syringe after the fluid is delivered. In particular, the syringe device comprises a hollow plunger which is extendable into a cylindrical barrel thereby forcing fluid from the barrel and through a needle attached to one end of the barrel. The hollow plunger is capable of receiving the retractable needle once the plunger is fully extended into the barrel.
Hypodermic syringes are commonly used to deliver fluids from the syringe to one or more internal areas of the patient. Health care professionals which use hypodermic syringes often risk infection if they accidentally are scratched or punctured by the needle after injections are completed. Therefore, contaminated hypodermic needles present a substantial health hazard to anyone who handles or uses a hypodermic needle. Accordingly, there exists a need to protect personnel from accidental skin puncture injuries from such contaminated needles as well as the need to provide a safe and efficient means for disposing of the needles.
Recently there has been increased emphasis placed in designing hypodermic syringes with extendable shields which project over the needle area after injections are completed. Such devices often involve manual manipulation of the shield over the needle after the injection is completed. It follows that when the shield is manually extended over the needle, the operator's hand or fingers often come in contact with the tip of the needle, thus causing risk of contamination. In an effort to solve the problem of having to manually extend the shield, many devices have built-in biasing mechanism which automatically extend a shield over the needle after the injection is completed. These devices help reduce accidental contact with the needle, but they do not completely prevent access of the operator to the needle as would be the case if the needle were retracted inside the syringe. An extendable shield may still leave the needle accessible to finger tips through the unsealed forward end of the sheath. Further, the needle tip may become exposed if the sheath is moved or displaced by a jarring force.
In an effort to overcome the problems associated with extendable sheathings, many conventional devices protect the operator by manually retracting the needle inside the syringe. As the plunger is pushed toward the end of the barrel, it couples onto one end of the retractable needle and by manually pulling the plunger, the needle is drawn from its extended position into the syringe barrel. The conventional method of retracting a needle into the barrel by manually retracting the plunger has many disadvantages. First, the plunger must make secure connection with one of the needles, often involving detailed and complicated mechanisms. Second, the needle must be manually drawn into the syringe, thereby involving a two-handed operation. One hand is needed to secure the syringe, while the other is used to withdraw the plunger relative to the syringe. Third, the needle is typically retracted only after it is withdrawn from the patient.
Although manual retraction of a needle is preferred over needle-sheathing devices, their complicated structure and cumbersome nature may leave them undesirable for many applications. In an effort to overcome the difficulty in having to manually retract the needle, many conventional devices use a triggering mechanism which releases the needle from its extended position to a position inside the syringe. Typical triggering mechanisms involve activating arms or levers placed on the outside of the syringe. When these external levers are activated, the needle is automatically drawn into the syringe by one or more biasing mechanisms. While external levers having automatic retraction mechanisms provide an easier means for retracting the needle, they are often unduly complicated to both manufacture and operate. The trigger mechanisms are often configured at a point distant from the plunger, thereby requiring the operator to move his or her hand from a convenient point on the plunger to a distal trigger location. Further, they may be inadvertently activated if the triggering mechanism is accidentally activated.
Although many safety syringes are becoming easier to operate, they are becoming equally more difficult to manufacture. It is important that a safety syringe be both convenient to operate and economical to manufacture. Accordingly, syringes which allow convenient retraction of the needle must also be easy and inexpensive to manufacture. Conventional safety syringes appear unable to achieve both objectives.